The solidification of the electrolyte provides an advantage for use in battery applications. In the case of the all-solid-battery system, the non-liquid nature of the electrolyte allows stacking of the battery cells in a single package without an ionic short circuit. Such a battery configuration decreases the dead-space between the single cells. In addition, this structure is suitable for applications requiring a high voltage and limited space, such as vehicle power sources.
In the basic structure of an exemplary all-solid-state battery the following layers are arranged in order: cathode current collector, cathode, solid electrolyte, anode, anode current collector. Further layers may be present—for example, a buffer layer may also be interposed at the cathode/solid electrolyte interface in order to enhance lithium-ion transfer at the interface, for a lithium all-solid-state battery.
As representative examples of known cathode active materials for lithium all-solid-state batteries, LiCo2 and LiFePO4 may be cited. The negative electrode active material may be, for example, a carbon active material or a metal/alloy-based active material.
Concerning the solid-state electrolyte for lithium all-solid-state batteries, a certain number of oxide-based or sulfide-based materials are known. Oxide-based solid electrolyte materials for lithium all-solid-state batteries typically contain Li and O, and often also a transition metal and/or metal/metalloid from group 13/14 of the Periodic Table (e.g. Al, Si, Ge), and/or phosphorus. Known materials in this context include LiPON (for example, Li2.9PO3.3N0.46), LiLaTiO (for example, Li0.34La0.51TiO3), LiLaZrO (for example, Li7La3Zr2O12). Compounds which have a NASICON mold structure can also be mentioned e.g. the compound denoted by general formula Li1+xAlxGe2-x(PO4)3 (0≤x≤2), or the compound denoted by general formula Li1+xAlxTi2-x(PO4)3 (0≤x≤2). Another possibility is a lithium borosilicate.
Concerning sulfide-based electrolyte materials for lithium all-solid-state batteries, known materials include ones containing Li, S, and commonly one or more of P, Si/Ge (also group 13 elements B, Al, Ga, In). Known possibilities include, for example, Li10GeP2S12, Li2S—P2S5 and Li2S—P2S5—LiI, Li2S—P2S5—Li2O, Li2S—P2S5-LO-LiI, Li2S—SiS2 and Li2S—SiS2—LiI, Li2S—SiS2—LiBr, Li2S—SiS2—LiCl, Li2S—SiS2—B2S3—LiI, Li2S—SiS2—P2S5—LiI, Li2S—B2S3, Li2S—P2S5—ZmSn (m and n being positive numbers, Z being Ge, Zn, or Ga), Li2S—GeS2 and Li2S—SiS2—Li3PO4, and Li2S—SiS2-LixMOy (where x and y are positive numbers, M is P, Si, Ge, B, aluminum, Ga, or In etc.) The description of the above “Li2S—P2S5” refers to sulfide solid electrolyte materials which use the material composition containing Li2S and P2S5 in varying relative amounts, the same naming convention referring to other descriptions hereinabove.
The cathode materials of sodium ion batteries, for example sodium layered oxides (NaxMO2, where M is a transition metal) and polyanion systems NaxM3(PO4)2P2O7, where M is a transition metal) are expected materials for a positive electrode in respect of their high capacity and ion diffusivity, leading to high power batteries. However, because of the high potential of sodium, the voltage of battery is low. Therefore their energy density may be limited.
Noguchi et al., in Electrochimica Acta 101 (2013) 59-65, studied all solid-state sodium batteries. A symmetrical structure was studied with Na3Zr2Si2PO12 (NASICON) as solid electrolyte, and Na3V2(PO4)3 (NVP) as active electrode material (anode and cathode). However, only a relatively low voltage of about 2.0 V could be produced.
Wang et al., in Electrochemistry Communications 11 (2009) 1834-1837, studied a rechargeable lithium battery, in which a copper (Cu) cathode in an aqueous electrolyte and a Li-anode in a non-aqueous electrolyte are linked via a lithium super-ionic conductor glass film (LISICON). In this mixed system Li—Cu, the dissolution/deposition process of metallic Cu was used as the cathode reaction. A problem here is however that with a low ion density of the liquid electrolyte (1-2 mol dm−3), there would be a low energy density of the battery.